Knife switch



Feb. 25, 1930. o. MORGER 1,748,724

KNIFE SWITCH Filed Nov. 9, 1925 Patented Feb. 25, 1930 UNITED STATES OTTO MORGER, OF BADEN, SVJITZERLAND, ASSIGNOR T AKTIENGESELLSCHAFT BROWN BOVERI AND GEE,

6F BAD-EN, SVITZERLAND KNIFE SVJZTCH Application filed November *3, Serial No. 67,753, and. in Germany December 8, 1924.

This invention relates to knife switches and the like and it has for its general object to provide a switch which will not open on the passage of an exceptionally large current, such as may result from a short-circuit.

Knife switches may be caused to open automatically on the passage of a large current due to a short-circuit, by reason of the powerful electro-dynamic forces set up, and to 0 prevent this it has hitherto been usual to employ pawls arranged in various ways. A1 rangements of this kind, however, complicate and increase the cost of construction and have been found in practice not to be entirely reliable.

The present invention contemplates using the increase of electro-dynamic force that occurs on the passage of a short-circuit current to assist in holding closed the switch. Thus these forces acting in the contact parts are utilized to hold closed the blade of the switch.

The invention will now be described with reference to the accompanying drawings wherein Fig. 1 shows a longitudinal elevation of one form,

Figs. 2 and 3 show end elevations of modified forms,

Fig. 4 shows a longitudinal elevation of part of a switch of a further modified form and Fig. 5 a plan thereof, and

Fig. 6 an end elevation of a further modi' tied form.

Referring to Fig. 1 the blade 6 is provided with a slot which at its inner end 2' bends towards the front edge of the blade and which embraces a pin or screw 0 on the contact member a when the switch is closed. One or both of the supporting insulators f and g I is or are flexibly mounted so as to be slightl movable toward and from the other, for example, ona cork or rubber disc or on a support provided with a oint. In the drawing the insulator f is shown mounted on a panel j by means of a rod which passes through a tapered hole Zin the panel, the said tapered hole permitting a slight movement of the insulator. Since the two contact members together with the insulators are forced apart when a heavy current due to a short-circuit passes the closed switch, the pin 0 presses with great force against the outer wall of the slot (Z with the result that the knife is frictionally held against the tendency to open. I

In the construction illustrated in Figs. 2 and 3 the contact members consist of springs a bent inwardly in the form of a loop or loops, the current entering at the inner end of the loop and leaving at the outer end. Since the current induces forces in the spring loops at tending to expand or spread the loops, the movable arms thereof will be pressed against the blade Z) with a pressure which increases with the strength of the current.

The springs a are arranged on either side of the blade I) and supporting means such as the screw or pin 0 shown in Fig. 2, or the rigid lateral abutments 6 shown in Fig. 3, prevents the outer arms of the loops from moving outwardly under the action of the heavy currents so that the whole of the loopexpanding pressure produced by the electrodynamic force is utilized as frictional pressure against the blade Z).

With the arrangement shown in Fig. 2 the blade slot may also be such as to enable it to engage the screw or pin 0 retentively, in a manner similar to that of the arrangement illustrated in Fig. 1. Therefore, when the switch is closed, the blade limits movement of the contact members in the longitudinal di rection of the blade as the electro-dynaniic force which tends to force them apart on the passage of a short-circuit current will be transferred to the blade and taken up by it as a tensile stress, thereby relieving the insulator mountings of the pressure.

in the modified embodiment illustrated Figs. i and 5, the blade 6 is provided with lateral retaining members It at its free end, so arranged as to overlap the outer margin of the contact member a; when the switch is closed. lVhen the contact member is forced outwardly on the passage of an abnormal current, the contact member is forcibly pressed the retaining member it, and the blade thcreq retained in engagement with the contact member. This feature may be combined with the loop arrangement illustrated in Figs. 2 and 3.

In the modified embodiment illustrated in Fig. 6, the movable switch-closing member is formed with two blades 7) which are connected in parallel spaced relationship by spacing bolts or pins 0, and the contact member a is formed as a double loop with its free arms toward the outer sides. The blades close against the outer arms of the loop against their spring tension. On the passage of an abnormal current, the electrodynamic forces tend to spread the loops, thus pressing the outer arms thereof against the blades with increased force, the blades being held against spreading by the spacer bolts 0. The feature iilustrated in Figs. 4 and 5 may be combined with this construction.

From the foregoing, accordingly, it will be observed that in addition to the movable blade or switclrclosing member, the switch has a contact or terminal member which is shiftable by the electrodynamic forces produced by a current passing the switch, so as to exert mechanical pressure on a movable switchclosing member in a fashion to retain the same in engagement with the contact memher.

What I claim is 1. A knife switch having a contact, a pin therethrough, and a blade having a slot to receive the pin such that on the passage of a short-circuit current the forces set up act to increase the pressure between the pin and the surface of the slot to oppose the opening of the switch.

2. A knife switch having a contact, a pin therethrough, and a blade having a slot to receive the pin and shaped to constitute a catch such that on the passage of a short-circuit current the forces set up act to increase the pressure between the pin and the surface of the slot to oppose the openin of the switch.

3. A knife switch having a contact consisting of a pair of springs each bent in the form of a loop with their free ends adjacent, a pin through the springs to support their other ends and prevent movement thereof, and a blade movable between the free ends of the springs and having a slot to receive the pin such that on the passage of a short-circuit current the forces set up act to increase the pressure between surfaces of the springs and the blade and between the pin and the surface of the slot to oppose the opening of the switch.

4. A knife switch having a contact mounted to have slight movement and consisting of a pair of springs each bent in the form of a loop with their free ends adjacent, a pin through the springs to support their other ends and prevent movement thereof, and a 'blade movable between the free ends of the springs and having a slot to engage the pin such that on the passage of a short-circuit current the forces set up act to increase the pressure between surfaces of the springs and the blade and between the pin and the surface of the slot to oppose the opening of the switch.

5. A knife switch having a contact consist ing of a pair of springs each bent in the form of a loop with their free ends adjacent, a in through the springs to support their ot er ends and prevent movement thereof, a blade movable between the free ends of the springs and having a slot of a size to receive the pin closely such that on the passage of a shortcircuit current the force set up tending to bend the terminals of the switch outwardly is taken up by the blade as a tensile stress thereby relieving the supporting insulators that carry the stationary contacts.

(3. In switch apparatus, complementary contact elements disposed for relative movement into and out of contacting relation with respect to each other, one of said elements being resilient and operable by virtue of its resiliency to retentively engage the other with a spring action, and means associated with one of said elements and being operable upon occurrence of abnormal current conditions in said apparatus to provide for retentive engagement of said elements supplementary to and independent of such engagement due to said spring action and being proportional in amount to the degree of occurring abnormal current conditions in said apparatus.

7. In switch apparatus, complementary contact elements disposed for relative movement into and out of contacting relation with rescpect to each other, means supporting one of said elements and providing for bodily movement of the same incident to occurrence of abnormal current conditions in said apparatus when said elements are operatively engaged, and means operable incident to such movement to provide for retention of said elements in engaged relation.

Dated this 23d day of October, 1925.

OTTO MORGER. 

